1. Field of Invention
The invention relates to an antenna structure and, in particular, to a multi-band antenna structure.
2. Related Art
The connections and communications in wireless personal area network (WPAN), wireless local area network (WLAN), and wireless wide area network (WWAN) or among various wireless devices can be implemented using the antennas therein.
Generally speaking, the antenna of a wireless device can be external or internal. For example, some laptop computers have external antennas on top of the screens or on PCMCIA cards. Since these external antennas are exposed to the environment, they are more expensive and susceptible to damages. The other design is to build the antenna directly inside the laptop computer.
The built-in antenna design can avoid some problems of the external antenna. For example, the appearance of the computer is better. The antenna is less likely to be damaged by accident. However, putting the antenna inside the limited space of a small computer device has several constraints. To fit into the allowed space, some operating bandwidths are sacrificed. Therefore, the allowed error rate of such antennas is very small, resulting in a higher cost for mass production. Therefore, how to design a new internal antenna structure to increase its bandwidth is an important goal for the manufacturers.